1. Field of Invention
The present invention pertains to isolation valves used in subsurface wells, and particularly to retrievable and large bore formation isolation valves.
2. Related Art
It is often desirable to isolate a portion of a well. For example, a portion of the well may be isolated during insertion or retrieval of a drill string. It may also be desirable to isolate a portion of a well during perforation operations, particularly during underbalanced completion operations. There are several devices and methods available to perforate a formation using underbalanced completion operations. Those include using special connectors such as “Completion Insertion and Retrieval under Pressure” connectors, placing formation isolation valves in the completion, and using wireline or coil tubing. However, each of those options has shortcomings, and none of those methods or devices allow, in the case of multiple production zones, flowing each zone individually for clean up and testing. Therefore, there is a continuing need for improved isolation devices.